1. Field of the Invention
The present invention relates to a clutch system comprising at least one clutch device for installation in a motor vehicle drive train between a drive unit and a transmission, the clutch device having at least one clutch arrangement which can be actuated by a pressure medium and which is operated by the action of an operating medium, the pressure medium being provided by a first pump arrangement and the operating medium being supplied to the clutch device by a second pump arrangement.
2. Description of the Related Art
The present invention is based on a clutch system with the basic design described in German Patent Applications No. 100 56 954.4 of Nov. 17, 2000 and No. 101 02 874.1 of Jan. 23, 2001, which claims the priority of German Patent Application No. 100 56 953.7 of Nov. 17, 2000. The contents of these German patent applications are incorporated in their entirety by reference in the disclosure of the present application and the proposals made in those documents are to be considered advantageous elaborations of the clutch system according to the invention discussed here.
The clutch system according to the present invention concerns a wet-running dual clutch system with two wet-running multi-disk clutch arrangements, which can be actuated hydraulically by slave cylinders integrated into the clutch device. The clutch device in question can be, for example, a clutch device according to a design of the applicant as described in U.S. patent application Ser. No. 09/678,442, filed on Oct. 2, 2000 (now U.S. Pat. No. 6,464,059), the entire contents of which are incorporated by reference in the disclosure of the present application.
For the actuation of the multi-disk clutch arrangements, a wet-running dual clutch system of this type requires a flow of pressure medium which, averaged over time, is low in terms of volume but high in terms of pressure. The clutch also requires, however, a comparatively high volume flow rate of the operating medium at comparatively low pressure to cool the friction linings or disks. In the interest of conserving energy, a separate specially adapted pump arrangement (pump) is used for each of these two volume streams, i.e., a first pump arrangement for providing a first medium as the pressure medium and a second pump arrangement for providing a second medium as the operating medium at comparatively low pressure. Because only a small volume flow rate, averaged over time, is required to develop the pressure needed for clutch actuation, a hydraulic accumulator may be provided downstream from the first pump arrangement in question to store the required hydraulic medium. The first pump arrangement therefore requires only a pump of comparatively low delivery volume.
For the clutch system of the present invention, the second medium provided by the second pump arrangement may be selectively fed to as the pressure medium to a least one pressure-medium slave cylinder of the clutch device to actuate the clutch arrangement assigned to the slave cylinder for the purpose of either engaging it (in the case of, for example, a clutch arrangement of the NORMALLY OPEN type) or disengaging it (in the case of, for example, a clutch arrangement of the NORMALLY CLOSED type).
By prefilling or partially filling the slave cylinder with the second medium provided by the second pump arrangement with the use of a bypass around the first pump arrangement, comparatively short switching times are obtained, and a first pump arrangement with an especially low delivery volume may be used. These advantages are derived from the fact that, to fill the slave cylinder of a wet-running clutch to increase the pressure from zero to approximately 20% of the maximum pressure, it is necessary to supply about 90% of the filling volume (merely by way of example) which the slave cylinder has at maximum pressure. A fraction of the maximum pressure on the order of magnitude cited (for example, 20%) can also be produced by a typical coolant pump such as the second pump arrangement. Accordingly, the second pump arrangement may be used to prefill or partially to fill the slave cylinder to a significant extent (e.g., to the above-cited 90% of its volume), whereas the first pump arrangement is used primarily to fill the slave cylinder from that point on to produce even higher pressures.
It is also within the scope of the present invention to connect the first pump arrangement downstream from the second pump arrangement, so that the medium received by first pump arrangement is already at an elevated pressure level created at the discharge of the second pump. The pressure increase which the first pump arrangement is therefore required to produce is smaller than that which would be required if the medium were being drawn in from the pressure equalization tank or the like. Because of the lower requirements with respect to pressure, an especially low-cost pressure pump may be used. Furthermore, a separate pressure filter in the pressure circuit may be omitted in this configuration.
One of the primary goals of the present invention is to design the first pump arrangement to provide a first volume flow rate at a first pressure level and to design the second pump arrangement to provide a second volume flow rate at a second pressure level, where, under normal operating conditions, the first volume flow rate will be smaller than the second volume flow rate and the first pressure level will be higher than the second pressure level.
As indicated above, the first pump arrangement is or can be connected by its suction side to a delivery side of the second pump arrangement to draw medium provided by the second pump arrangement and to provide it as pressure medium on a higher pressure level.
As mentioned above, the second pump arrangement may be connected to the slave cylinder in parallel with the first pump arrangement to allow the slave cylinder to be prefilled or partially filled with the second medium provided by the second pump arrangement.
In this context, the slave cylinder is or may be connected to the delivery side of the second pump arrangement by an open loop/closed loop valve arrangement.
Alternatively, the slave cylinder may be connected to the delivery side of the second pump arrangement such that it bypasses an open loop/closed loop valve arrangement installed between the first pump arrangement and the slave cylinder. This latter design allows an open loop/closed loop valve arrangement with a very small effective flow cross section to be used without limiting or impairing the reduction in the switching times obtained as a result of the prefilling or partial filling.
Since the slave cylinder can be filled additionally with pressure medium provided by the first pump arrangement via the open loop/closed loop valve arrangement, an operating pressure can be reached which is higher than the delivery pressure of the second pump arrangement.
In conjunction with the prefilling or partial filling, it is also proposed that a section of the operating medium system downstream from the second pump arrangement have an effective flow cross section which is dimensioned such that a pressure level is reached on the delivery side of the second pump arrangement which allows the slave cylinder to be partially filled or prefilled to a technically relevant extent the second with medium provided by the second pump arrangement. Alternatively, at least one pressure-adjusting or pressure-increasing device may be provided in a section of the operating medium system downstream from the second pump arrangement, for setting a pressure level on the delivery side of the second pump arrangement which allows the slave cylinder to be partially filled or prefilled to a technically relevant extent with medium provided by the second pump arrangement. The pressure adjusting or pressure increasing device may comprise at least one throttle or orifice plate and/or at least one pressure-relief valve or pressure-reducing valve. Furthermore, the pressure-adjusting or pressure-increasing device may be switchable between a first state, in which it has the effect of adjusting the pressure level, and a second state, in which it does not have an adjusting effect on the pressure level. In the second state, the operating medium may then be supplied (to cool the friction linings or disks, for example) without being affected or hindered by the pressure-adjusting or pressure-increasing device of the clutch device.
The manner in which the second pump arrangement is connected to the slave cylinder for the prefilling or partial filling may be effected by many different designs. Accordingly, the slave cylinder may be connected via a pilot valve arrangement to the second pump arrangement. When this pilot valve arrangement is in a first state, it allows the medium provided by the second pump arrangement to pass to the slave cylinder partially to fill or to prefill the slave cylinder. When the pilot valve arrangement is in a second valve state, it allows essentially none of the medium provided by the second pump arrangement to pass through to the slave cylinder. The valve arrangement may, for example, comprise a 3/2-port directional valve with a further valve state in which it allows medium to flow out of the slave cylinder to empty it.
According to another embodiment, the slave cylinder is connected to the second pump arrangement via a non-return valve arrangement. The nonreturn valve arrangement may also be provided in combination with a pilot valve arrangement.
At least one pilot valve may be assigned to the slave cylinder to serve as a drain valve. When this valve, which could possibly be called an emergency discharge valve, is in a first state, it allows the medium to flow out of the slave cylinder to empty it and/or allows medium supplied by the second pump arrangement and supplied to a feed side of the slave cylinder to flow away from the feed side to hold the slave cylinder in an empty or partially emptied state. Alternatively, the effective discharge flow cross section of the open loop/closed loop valve arrangement assigned to the slave cylinder may be made large enough to allow the second medium provided by the second pump arrangement and supplied to the feed side of the slave cylinder to flow away from the feed side in order to keep the slave cylinder in an emptied or partially emptied state.
A non-return valve arrangement may be inserted between the first pump arrangement and the slave cylinder such that the discharge from a pressure reservoir via the first or second pump arrangement is blocked.
As mentioned above, the clutch arrangement may be a wet-running clutch arrangement, and the clutch of the wet-running type can be operated by the action of the operating medium. Furthermore, the operating medium may comprise an operating fluid such as a coolant. As already mentioned, the clutch arrangement may be designed as a multi-disk clutch arrangement.
With respect to the pressure medium, a hydraulic pressure medium, especially a hydraulic oil, which can also possibly serve as a coolant, will be used in most cases.
The clutch device can be multi-clutch arrangement, especially a dual clutch device, which has a first clutch arrangement and a second clutch arrangement. The first clutch arrangement has at least a first slave cylinder, and the second clutch arrangement has at least a second slave cylinder. According to the inventive proposal, medium provided by the second pump arrangement can be supplied to the two slave cylinders independently of each other, especially for the purpose of achieving the advantages discussed above.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.